Sun dials in various forms have been known and used for centuries to assist in more accurately determining sun time during daylight hours. In their simplest form these sun dials consisted of little more than a vertically upstanding member called a gnomon which upon the incidence of the sun's rays cast a shadow directed upon and along a dial with movement of the sun to establish a line of demarcation between the shadow and areas of direct impingement of the sun's rays. While the early sun dials gave some indications of the same sun time on successive days they were too simplistic to take into account differences in mean time and solar time as a function of the day of the year, locations within a time zone and other variables.
More recently, increasingly sophisticated sun dials were developed and used for many years which endeavored to take into account some of the variables which were not considered in the earlier devices. Certain of the improved devices have employed a dial which is angularly adjustable to compensate for a combination of calculated differences between the sun and clock time in the different seasons of the year. In many instances users have been unable to accurately calculate the required combination of corrections to effect substantial accuracy. Nor can a combined calculation be supplied by a sun dial manufacturer since the magnitude and combination of these calculated adjustments differ in some instances with the time of the year and in other instances with location on the surface of the earth.
In other instances efforts have been made to supply a sun dial having an attachment adapted to compensate at least for differences in mean time and solar time as a function of the day of the year in either the northern or southern hemisphere such that at least this correction from sun time is made by setting the device to the appropriate day of the year with a resulting correction being imparted as between the gnomon and the dial in relation to the path of the sun. More generalized corrections have been attempted by providing a gnomon having a calculated configuration which endeavors to take into account differences between mean time and solar time as a function of the time of the year due to differences in the sun's declination.
To Applicant's knowledge all of the above prior art devices have had serious limitations in their ability to be located at any position on the earth's surface and have the self-contained capability of accurate adjustment to take into account all of the different variables necessary to convert sun time to clock time at any desired location on the surface of the earth.